Nanoparticle hydrides can be manufactured through milling of existing hydrides or milling of metals which can be later exposed to hydrogen to form a hydride. Current methods for producing nanoparticle hydrides revolve around high-energy ball milling or condensation reactions from a heated material. In general, complex alloy hydrides must start from a mixed ingot, and then be processed into a workable material. Ingot materials have very low surface area and are very slow at hydrogen absorption. Milling these materials down can introduce contaminants and often takes hours to days to accomplish. In addition to this, milling must be done as a batch process—ultimately limiting the production rate compared to a continuous process.
Nanoscale hydrides can also be prepared by a number of different hydrogen-driven processes, such as hydrogen decrepitation, disproportionation-recombination, and metathesis reactions. A commercial scale hydrogen decrepitation process was originally developed to produce nanoscale rare earth alloys for high remanence and coercivity magnets (see Harris et al., “The hydrogen decrepitation of an Nd15Fe77B8 magnetic alloy,” Journal of the Less Common Metals, Volume 106, Issue 1, March 1985). More recently, a similar process was proposed to produce nanoscale hydrides (see Graetz et al., “Nanoscale Energy Storage Materials Produced by Hydrogen-Driven Metallurgical Reactions,” Adv. Eng. Mat. 7, 597, 2005).
Gas-phase condensation and ballistic consolidation could also be used to prepare nanoparticles. This technique has been used to prepare nanoscale materials (Si and Ge) for lithium battery anodes (see Graetz et al., “Highly Reversible Lithium Storage in Nanostructured Silicon,” Electrochem. Solid-State Lett., 6, A194, 2003). In this process, a charge is heated in a tungsten basket or crucible and evaporated into a gas stream. The atoms cool rapidly and nucleate nanocrystals in the gas. The agglomerated nanoparticles become entrained in the gas and form a film of ballistically consolidated nanocrystals when they hit the substrate at high speed.
Improvements are desired for the commercial production of nanoparticle hydrides, which have many industrial uses.